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PHY303LEXAM1 - Version 109 Exam 01 Chiu(58295 This...

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Version 109 – Exam 01 – Chiu – (58295) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Two uncharged metal balls, Z and X , stand on insulating glass rods. A third ball, carrying a positive charge, is brought near the ball X as shown in the figure. A conducting wire is then run between Z and X and then removed. Finally the third ball is removed. X Z + conducting wire When all this is finished 1. ball Z is neutral and ball X is negative. 2. ball Z is positive and ball X is neutral. 3. balls Z and X are both negative, but ball X carries more charge than ball Z . 4. balls Z and X are both positive. 5. balls Z and X are both negative, but ball Z carries more charge than ball X . 6. ball Z is negative and ball X is positive. 7. ball Z is positive and ball X is negative. correct 8. ball Z is neutral and ball X is positive. 9. ball Z is negative and ball X is neutral. 10. balls Z and X are still uncharged. Explanation: When the conducting wire is run between Z and X , some positive charge flows from X to Z under the influence of the positive charge of the third ball. Therefore, after the wire is removed, Z is charged positive and X is charged negative. 002 10.0 points Two charged particles of equal magnitude (+ Q and + Q ) are fixed at opposite corners of a square that lies in a plane (see figure be- low). A test charge q is placed at a third corner. + Q q + Q What is the direction of the force on the test charge due to the two other charges? 1. 2. 3. 4. 5. correct 6. 7. 8. Explanation: The force between charges of the same sign is repulsive. The force between charges with opposite signs is attractive.
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Version 109 – Exam 01 – Chiu – (58295) 2 + Q q + Q The resultant force is the sum of the two vectors in the figure above. Therefore the correct choice is 003 10.0 points Four point charges are placed at the four cor- ners of a square. Each side of the square has a length L . q 1 = q q 3 = q q 2 = q q 4 = q P L L Find the magnitude of the electric force on q 2 due to all three charges q 1 , q 3 and q 4 . Given L = 1 m and q = 1 . 73 μ C. 1. 0.0157246 2. 0.030333 3. 0.0446555 4. 0.0353804 5. 0.0163124 6. 0.0249351 7. 0.0143023 8. 0.0403483 9. 0.0380497 10. 0.021744 Correct answer: 0 . 0403483 N. Explanation: F 1 F 4y F 4 F 3 F 4x q 2 From the above figure, we see that F 1 = k q 2 L 2 ˆ ı = ( 8 . 98755 × 10 9 N · m 2 / C 2 ) × (1 . 73 × 10 6 C) 2 (1 m) 2 = 0 . 0268988 N F 3 = k q 2 L 2 ˆ = ( 8 . 98755 × 10 9 N · m 2 / C 2 ) × (1 . 73 × 10 6 C) 2 (1 m) 2 = 0 . 0268988 N F 4 x = k q 2 2 L 2 1 2 = 8 . 98755 × 10 9 N · m 2 / C 2 2 · (1 m) 2 × (1 . 73 × 10 6 C) 2 2 = 0 . 00951018 N F 4 y = k q 2 2 L 2 1 2 = 8 . 98755 × 10 9 N · m 2 / C 2 2 · (1 m) 2 × (1 . 73 × 10 6 C) 2 2 = 0 . 00951018 N bardbl vector F bardbl 2 = ( F 1 + F 4 x ) 2 + ( F 3 + F 4 y ) 2 = ( 0 . 0268988 N + 0 . 00951018 N) 2 + ( 0 . 0268988 N + 0 . 00951018 N) 2 so that bardbl vector F bardbl = 0 . 00162798 N 2 = 0 . 0403483 N .
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